A Guide to Polysaccharide-Based Hydrogel Bioinks for 3D Bioprinting Applications

Thiol-ene click chemistry: Enabling 3D printing of natural-based inks for biomedical applications

Over the last decade, 3D bioprinting has gained increasing popularity, being a technique capable of producing well-defined tissue-like structures. One of its most groundbreaking features is the ability to create personalized therapies tailored to the specific demands of individual patients. However, challenges including the selection of materials and crosslinking strategies, still need to be addressed to enhance ink characteristics and develop robust biomaterials. Herein, the authors showcase the potential of overcoming these challenges, focusing on the use of versatile, fast, and selective thiol-ene click chemistry to formulate inks for 3D bioprinting. The exploration of natural polymers, specifically proteins and polysaccharides, will be discussed and highlighted, outlining the advantages and disadvantages of this approach. Leveraging advanced thiol-ene click chemistry and natural polymers in the development of 3D printable bioinks may face the current challenges and is envisioned to pave the way towards innovative and personalized biomaterials for biomedical applications.

Innovating chitosan-based bioinks for dermal wound healing: Current progress and future prospects

The field of three-dimensional (3D) bio/printing, known as additive manufacturing (AM), heavily relies on bioinks possessing suitable mechanical properties and compatibility with living cells. Among the array of potential hydrogel precursor materials, chitosan (CS) has garnered significant attention due to its remarkable physicochemical and biological attributes. These attributes include biodegradability, nontoxicity, antimicrobial properties, wound healing promotion, and immune system activation, making CS a highly appealing hydrogel-based bioink candidate. This review explores the transformative potential of CS-based bioink for enhancing dermal wound healing therapies. We highlight CS's unique qualities that make it an optimal choice for bioink development. Advancements in 3D bio/printing technology for tissue engineering (TE) are discussed, followed by an examination of strategies for CS-based bioink formulation and their impacts on wound healing. To address the progress in translating advanced wound healing from lab to clinic, we highlight the current and ongoing research in CS-based bioink for 3D bio/printing in skin wound healing applications. Finally, we explore current evidence, commercialization prospects, emerging innovations like 4D printing, and the challenges and future directions in this promising field.

Recent advances in 3D bioprinted polysaccharide hydrogels for biomedical applications: A comprehensive review

Polysaccharide hydrogels, which can mimic the natural extracellular matrix and possess appealing physicochemical and biological characteristics, have emerged as significant bioinks for 3D bioprinting. They are highly promising for applications in tissue engineering and regenerative medicine because of their ability to enhance cell adhesion, proliferation, and differentiation in a manner akin to the natural cellular environment. This review comprehensively examines the fabrication methods, characteristics, and applications of polysaccharide hydrogel-driven 3D bioprinting, underscoring its potential in tissue engineering, drug delivery, and regenerative medicine. To contribute pertinent knowledge for future research in this field, this review critically examines key aspects, including the chemistry of carbohydrates, manufacturing techniques, formulation of bioinks, and characterization of polysaccharide-based hydrogels. Furthermore, this review explores the primary advancements and applications of 3D-printed polysaccharide hydrogels, encompassing drug delivery systems with controlled release kinetics and targeted therapy, along with tissue-engineered constructs for bone, cartilage, skin, and vascular regeneration. The use of these 3D bioprinted hydrogels in innovative research fields, including disease modeling and drug screening, is also addressed. Despite notable progress, challenges, including modulating the chemistry and properties of polysaccharides, enhancing bioink printability and mechanical properties, and achieving long-term in vivo stability, have been highlighted.

Synthesis and characterization of dextran palmitate for extrusion 3D printing

The fabrication of objects with complex shape and geometry has been greatly facilitated with the advancements in additive manufacturing. While synthetic polymers like ABS and PLA have found widespread use in extrusion 3D printing, other biobased thermoplastics that are both biodegradable and biocompatible could offer strategic advantages over traditional synthetic materials. In this work dextran of low (20 kDa) and medium (40 kDa) molecular weight (MW) was modified with palmitic acid to obtain meltable polymers for extrusion 3D printing/fused deposition modeling additive manufacturing. The dextran derivatives were characterized by FTIR, NMR and elemental analysis. The degree of substitution (DS) varied between 0.94 ± 0.31 and 1.36 ± 0.16. Our findings reveal a melting temperature near 40 °C, independent of the DS or MW. Extrudability varied depending on the DS. Cubes with dimensions of 15 × 15 × 10 mm3 were printed from the dextran palmitate. The swelling degree of the cubes in water remained limited, up to 0.17 ± 0.02 g/g. This work demonstrates the great potential of dextran palmitate as biobased and biodegradable polymers for 3D printing for future applications in human health.

3D Bioprinting and Artificial Intelligence-Assisted Biofabrication of Personalized Oral Soft Tissue Constructs

Regeneration of oral soft tissue defects, including mucogingival defects associated with the recession or loss of gingival and/or mucosal tissues around teeth and implants, is crucial for restoring oral tissue form, function, and health. This study presents a novel approach using three-dimensional (3D) bioprinting to fabricate individualized grafts with precise size, shape, and layer-by-layer cellular organization. A multicomponent polysaccharide/fibrinogen-based bioink is developed, and bioprinting parameters are optimized to create shape-controlled oral soft tissue (gingival) constructs. Rheological, printability, and shape-fidelity assays, demonstrated the influence of thickener concentration and print parameters on print resolution and shape fidelity. Artificial intelligence (AI)-derived tool enabled streamline the iterative bioprinting parameter optimization and analysis of the interaction between the bioprinting parameters. The cell-laden polysaccharide/fibrinogen-based bioinks exhibited excellent cellular viability and shape fidelity of shape-controlled, full-thickness gingival tissue constructs over the 18-day culture period. While variations in thickener concentrations within the bioink minimally impact the cellular organization and morphogenesis (gingival epithelial, connective tissue, and basement membrane markers), they influence the shape fidelity of the bioprinted constructs. This study represents a significant step toward the biofabrication of personalized soft tissue grafts, offering potential applications in the repair and regeneration of mucogingival defects associated with periodontal disease and dental implants.

Self-healing, 3D printed bioinks from self-assembled peptide and alginate hybrid hydrogels

There is a pressing need for new cell-laden, printable, biomaterials that are rigid and highly biocompatible. These materials can mimic stiffer tissues such as cartilage, fibrotic tissue and cancer microenvironments, and thus have exciting applications in regenerative medicine, wound healing and cancer research. Self-assembled peptides (SAPs) functionalised with aromatic groups such as Fluorenyl-9-methoxycarbonyl (Fmoc) show promise as components of these biomaterials. However, the harsh basic conditions often used to solubilise SAPs leads to issues with toxicity and reproducibility. Here, we have designed a hybrid material comprised of self-assembled Fmoc-diphenylalanine (Fmoc-FF) assemblies dispersed throughout a sodium alginate matrix and investigated the influence of different organic solvents as peptide solubilising agents. Bioinks fabricated from peptides dissolved in 1,1,1,3,3,3-Hexafluoro-2-propanol (HFIP) showed improved biocompatibility compared to those made from Dimethyl Sulfoxide (DMSO) peptide stocks, due to the increased volatility and reduced surface tension of HFIP, allowing for more efficient expulsion from the system. Through optimisation of assembly and solvent conditions we can generate hybrid bioinks with stiffnesses up to 8 times greater than sodium alginate alone that remain highly printable, even when laden with high concentrations of cells. In addition, the shear-thinning nature of the self-assembled peptide assemblies gave the hybrid bioinks highly desirable self-healing capabilities. Our developed hybrid materials allow the bioprinting of materials previously considered too stiff to extrude without causing shear induced cytotoxicity with applications in tissue engineering and biosensing.

Optimization of chitosan-gelatin-based 3D-printed scaffolds for tissue engineering and drug delivery applications

The combination of biocompatible materials and advanced three-dimensional (3D) additive manufacturing technologies holds great potential in the development of finely tuned complex scaffolds with reproducible macro- and micro-structural characteristics for biomedical applications, such as tissue engineering and drug delivery. In this study, biocompatible printable inks based on chitosan, collagen and gelatin were developed and 3D-printed with a pneumatic-based extrusion printer. The printability of various chitosan-gelatin (CS-Gel) hydrogel inks was assessed by evaluating the quality of the printed constructs. The inks required an extrusion pressure of 150 ± 40 MPa with G22 and G25 nozzles for optimal printing. Inks with low chitosan concentrations (<4% w/v) exhibited poor printability, while inks with 4 % w/v chitosan and 1 % w/v gelatin (CG) demonstrated satisfactory extrusion and printing quality. The addition of collagen (0.1 % w/v) to the optimized ink (CGC) did not compromise printability. Post-printing stabilization using KOH produced self-supporting scaffolds with consistent morphological integrity, while weaker bases like NaOH/EtOH and ammonia vapors resulted in lower pore sizes and reduced structural stability. Water evaporation studies showed that neutralized samples had slower evaporation rates due to the strong intermolecular interactions formed during the neutralization process, contributing to a stable crosslinked network. FTIR spectra confirmed the formation of polyelectrolyte complexes in the CS-Gel and CS-Gel-Collagen blends, further enhancing structural stability. Swelling tests indicated that neutralized constructs maintained stability in different pH environments, with KOH-treated samples exhibiting the lowest swelling ratios and the highest structural stability. After optimizing the ink composition, 10 wt% Levofloxacin was loaded in the constructs as a model antibiotic and it's in vitro release rate was quantified. Drug loading was approximately 4 % for both ink compositions GC and CGC. CG Levo released over 80 % of levofloxacin within the first hour, reaching full release in 24 h, indicating inadequate control, while CGK Levo exhibited slower initial release (55 % in 15 min) followed by stabilized release after 4 h, likely due to controlled diffusion from expanded constructs. These findings demonstrate that the developed hydrogel inks and optimized printing parameters can produce scaffolds suitable for tissue engineering applications. Finally, the cell compatibility of the 3D-printed constructs was confirmed with MTT assay on fibroblasts and the antimicrobial activity of the drug-loaded constructs was tested against E. coli and S. aureus, showing an increase of the bacteria free zone from 8 ± 0.4 mm of the control against E. coli up to 16.4 ± 0.37 mm in the presence of the KOH-treated CG Levo printed construct.

Biobased hydrogel bioinks of pectin, nanocellulose and lysozyme nanofibrils for the bioprinting of A375 melanoma cell-laden 3D in vitro platforms

Melanoma is one of the most aggressive types of skin cancer, and the need for advanced platforms to study this disease and to develop new treatments is rising. 3D bioprinted tumor models are emerging as advanced tools to tackle these needs, with the design of adequate bioinks being a fundamental step to address this challenging process. Thus, this work explores the synergy between two biobased nanofibers, nanofibrillated cellulose (NFC) and lysozyme amyloid nanofibrils (LNFs), to create pectin nanocomposite hydrogel bioinks for the 3D bioprinting of A375 melanoma cell-laden living constructs. The incorporation of LNFs (5, 10 or 15 wt%) on a pectin-NFC suspension originates inks with enhanced rheological properties (shear viscosity and yield point) and proper shear-thinning behavior. The crosslinked hydrogels mimic the stiffness of melanoma tissues, being stable under physiological and cell-culture conditions, and non-cytotoxic towards A375 melanoma cells. P-NFC-LNFs (10 %) reveals good printability (Pr = 0.89) and printing accuracy (51 ± 2 %), and when loaded with A375 cells (3 × 106 cells mL-1) the bioink originates 3D-constructs with high cell viability (92 ± 1 %) after 14 days. The potential of the constructs as 3D in vitro platforms is corroborated by a drug-screening test with doxorubicin, where cells within the model displayed high sensitivity to the drug.

Targeting inflammation with hyaluronic acid-based micro- and nanotechnology: A disease-oriented review

Inflammation is a pivotal immune response in numerous diseases and presents therapeutic challenges. Traditional anti-inflammatory drugs and emerging cytokine inhibitors encounter obstacles such as limited bioavailability, poor tissue distribution, and adverse effects. Hyaluronic acid (HA), a versatile biopolymer, is widely employed to deliver therapeutic agents, including anti-inflammatory drugs, genes, and cell therapies owing to its unique properties, such as hydrophilicity, biodegradability, and safety. HA interacts with cell receptors to initiate processes such as angiogenesis, cell proliferation, and immune regulation. HA-based drug delivery systems offer dual strategies for effective inflammation management, capitalizing on passive and active mechanisms. This synergy permits the mitigation of inflammation by lowering the doses of anti-inflammatory drugs and their off-target adverse effects. A diverse array of micro- and nanotechnology techniques enable the fabrication of tailored HA-engineered systems, including hydrogels, microgels, nanogels, microneedles, nanofibers, and 3D-printed scaffolds, for diverse formulations and administration routes. This review explores recent insights into HA pharmacology in inflammatory conditions, material design, and fabrication methods, as well as its applications across a spectrum of inflammatory diseases, such as atherosclerosis, psoriasis, dermatitis, wound healing, rheumatoid arthritis, osteoarthritis, inflammatory bowel disease, and colitis, highlighting its potential for clinical translation.

Indirect prediction of the 3D printability of polysaccharide gels using multiple machine learning (ML) models

In this paper, the capabilities of NIR spectroscopy and LF-NMR data were compared for rapidly predicting the rheological properties of polysaccharide gels and assessing their printability. Seven machine learning (ML) models were established for rheological property prediction based on partial least squares regression (PLSR), support vector regression (SVR), back propagation artificial neural network (BPANN), one-dimensional convolutional neural network (1D CNN), recurrent neural network (RNN), long short-term memory (LSTM), and Transformer. The results showed that among the seven models, the SVR, BPANN, and 1D CNN models based on NIR spectroscopy effectively predicted the rheological parameters of polysaccharide gels, with the highest R2 in the prediction set reaching 0.9796 and the highest RPD reaching 7.0708. For most polysaccharide gels, using the LF-NMR relaxation time distribution curves provided better predictions of rheological properties than using transverse relaxation time and peak area. Among the seven models, the PLSR, SVR, 1D CNN, and Transformer models effectively predicted the rheological characteristics based on LF-NMR parameters, with the highest R2 in the prediction set reaching 0.9869 and the highest RPD reaching 8.7220. This study successfully established a prediction system for the rheological behaviors and 3D printing performance of polysaccharide gels using NIR spectroscopy and LF-NMR data combined with ML methods, achieving an intelligent assessment of the 3D printing behavior of polysaccharide gels.

Natural Regenerative Hydrogels for Wound Healing

Regenerative hydrogels from natural polymers have come forth as auspicious materials for use in regenerative medicine, with interest attributed to their intrinsic biodegradability, biocompatibility, and ability to reassemble the extracellular matrix. This review covers the latest advances in regenerative hydrogels used for wound healing, focusing on their chemical composition, cross-linking mechanisms, and functional properties. Key carbohydrate polymers, including alginate, chitosan, hyaluronic acid, and polysaccharide gums, including agarose, carrageenan, and xanthan gum, are discussed in terms of their sources, chemical structures and specific properties suitable for regenerative applications. The review further explores the categorization of hydrogels based on ionic charge, response to physiological stimuli (i.e., pH, temperature) and particularized roles in wound tissue self-healing. Various methods of cross-linking used to enhance the mechanical and biological performance of these hydrogels are also examined. By highlighting recent innovations and ongoing challenges, this article intends to give a detailed understanding of natural hydrogels and their potential to revolutionize regenerative medicine and improve patient healing outcomes.

Silk Fibroin-Enriched Bioink Promotes Cell Proliferation in 3D-Bioprinted Constructs

Three-dimensional (3D) bioprinting technology enables the controlled deposition of cells and biomaterials (i.e., bioink) to easily create complex 3D biological microenvironments. Silk fibroin (SF) has recently emerged as a compelling bioink component due to its advantageous mechanical and biological properties. This study reports on the development and optimization of a novel bioink for extrusion-based 3D bioprinting and compares different bioink formulations based on mixtures of alginate methacrylate (ALMA), gelatin and SF. The rheological parameters of the bioink were investigated to predict printability and stability, and the optimal concentration of SF was selected. The bioink containing a low amount of SF (0.002% w/V) was found to be the best formulation. Light-assisted gelation of ALMA was exploited to obtain the final hydrogel matrix. Rheological analyses showed that SF-enriched hydrogels exhibited greater elasticity than SF-free hydrogels and were more tolerant to temperature fluctuations. Finally, MG-63 cells were successfully bioprinted and their viability and proliferation over time were analyzed. The SF-enriched bioink represents an excellent biomaterial in terms of printability and allows high cell proliferation over a period of up to 3 weeks. These data confirm the possibility of using the selected formulation for the successful bioprinting of cells into extracellular matrix-like microenvironments.

Valorization of Grain and Oil By-Products with Special Focus on Hemicellulose Modification

Hemicellulose is one of the most important natural polysaccharides in nature. Hemicellulose from different sources varies in chemical composition and structure, which in turn affects the modification effects and industrial applications. Grain and oil by-products (GOBPs) are important raw materials for hemicellulose. This article reviews the modification methods of hemicellulose in GOBPs. The effects of chemical and physical modification methods on the properties of GOBP hemicellulose biomaterials are evaluated. The potential applications of modified GOBP hemicellulose are discussed, including its use in film production, hydrogel formation, three-dimensional (3D) printing materials, and adsorbents for environmental remediation. The limitations and future recommendations are also proposed to provide theoretical foundations and technical support for the efficient utilization of these by-products.

3D Printing of Polysaccharide-Based Hydrogel Scaffolds for Tissue Engineering Applications: A Review

In tissue engineering, 3D printing represents a versatile technology employing inks to construct three-dimensional living structures, mimicking natural biological systems. This technology efficiently translates digital blueprints into highly reproducible 3D objects. Recent advances have expanded 3D printing applications, allowing for the fabrication of diverse anatomical components, including engineered functional tissues and organs. The development of printable inks, which incorporate macromolecules, enzymes, cells, and growth factors, is advancing with the aim of restoring damaged tissues and organs. Polysaccharides, recognized for their intrinsic resemblance to components of the extracellular matrix have garnered significant attention in the field of tissue engineering. This review explores diverse 3D printing techniques, outlining distinctive features that should characterize scaffolds used as ideal matrices in tissue engineering. A detailed investigation into the properties and roles of polysaccharides in tissue engineering is highlighted. The review also culminates in a profound exploration of 3D polysaccharide-based hydrogel applications, focusing on recent breakthroughs in regenerating different tissues such as skin, bone, cartilage, heart, nerve, vasculature, and skeletal muscle. It further addresses challenges and prospective directions in 3D printing hydrogels based on polysaccharides, paving the way for innovative research to fabricate functional tissues, enhancing patient care, and improving quality of life.

Gelatin Methacryloyl (GelMA)-Based Biomaterial Inks: Process Science for 3D/4D Printing and Current Status

Tissue engineering for injured tissue replacement and regeneration has been a subject of investigation over the last 30 years, and there has been considerable interest in using additive manufacturing to achieve these goals. Despite such efforts, many key questions remain unanswered, particularly in the area of biomaterial selection for these applications as well as quantitative understanding of the process science. The strategic utilization of biological macromolecules provides a versatile approach to meet diverse requirements in 3D printing, such as printability, buildability, and biocompatibility. These molecules play a pivotal role in both physical and chemical cross-linking processes throughout the biofabrication, contributing significantly to the overall success of the 3D printing process. Among the several bioprintable materials, gelatin methacryloyl (GelMA) has been widely utilized for diverse tissue engineering applications, with some degree of success. In this context, this review will discuss the key bioengineering approaches to identify the gelation and cross-linking strategies that are appropriate to control the rheology, printability, and buildability of biomaterial inks. This review will focus on the GelMA as the structural (scaffold) biomaterial for different tissues and as a potential carrier vehicle for the transport of living cells as well as their maintenance and viability in the physiological system. Recognizing the importance of printability toward shape fidelity and biophysical properties, a major focus in this review has been to discuss the qualitative and quantitative impact of the key factors, including microrheological, viscoelastic, gelation, shear thinning properties of biomaterial inks, and printing parameters, in particular, reference to 3D extrusion printing of GelMA-based biomaterial inks. Specifically, we emphasize the different possibilities to regulate mechanical, swelling, biodegradation, and cellular functionalities of GelMA-based bio(material) inks, by hybridization techniques, including different synthetic and natural biopolymers, inorganic nanofillers, and microcarriers. At the close, the potential possibility of the integration of experimental data sets and artificial intelligence/machine learning approaches is emphasized to predict the printability, shape fidelity, or biophysical properties of GelMA bio(material) inks for clinically relevant tissues.

Unlocking the Potential of Stem Cell Microenvironments In Vitro

The field of regenerative medicine has recently witnessed groundbreaking advancements that hold immense promise for treating a wide range of diseases and injuries. At the forefront of this revolutionary progress are stem cells. Stem cells typically reside in specialized environments in vivo, known as microenvironments or niches, which play critical roles in regulating stem cell behavior and determining their fate. Therefore, understanding the complex microenvironments that surround stem cells is crucial for advancing treatment options in regenerative medicine and tissue engineering applications. Several research articles have made significant contributions to this field by exploring the interactions between stem cells and their surrounding niches, investigating the influence of biomechanical and biochemical cues, and developing innovative strategies for tissue regeneration. This review highlights the key findings and contributions of these studies, shedding light on the diverse applications that may arise from the understanding of stem cell microenvironments, thus harnessing the power of these microenvironments to transform the landscape of medicine and offer new avenues for regenerative therapies.

Glycosaminoglycans' Ability to Promote Wound Healing: From Native Living Macromolecules to Artificial Biomaterials

Glycosaminoglycans (GAGs) are important for the occurrence of signaling molecules and maintenance of microenvironment within the extracellular matrix (ECM) in living tissues. GAGs and GAG-based biomaterial approaches have been widely explored to promote in situ tissue regeneration and repair by regulating the wound microenvironment, accelerating re-epithelialization, and controlling ECM remodeling. However, most approaches remain unacceptable for clinical applications. To improve insights into material design and clinical translational applications, this review highlights the innate roles and bioactive mechanisms of native GAGs during in situ wound healing and presents common GAG-based biomaterials and the adaptability of application scenarios in facilitating wound healing. Furthermore, challenges before the widespread commercialization of GAG-based biomaterials are shared, to ensure that future designed and constructed GAG-based artificial biomaterials are more likely to recapitulate the unique and tissue-specific profile of native GAG expression in human tissues. This review provides a more explicit and clear selection guide for researchers designing biomimetic materials, which will resemble or exceed their natural counterparts in certain functions, thereby suiting for specific environments or therapeutic goals.

Reasoning on Pore Terminology in 3D Bioprinting

Terminology is pivotal for facilitating clear communication and minimizing ambiguity, especially in specialized fields such as chemistry. In materials science, a subset of chemistry, the term "pore" is traditionally linked to the International Union of Pure and Applied Chemistry (IUPAC) nomenclature, which categorizes pores into "micro", "meso", and "macro" based on size. However, applying this terminology in closely-related areas, such as 3D bioprinting, often leads to confusion owing to the lack of consensus on specific definitions and classifications tailored to each field. This review article critically examines the current use of pore terminology in the context of 3D bioprinting, highlighting the need for reassessment to avoid potential misunderstandings. We propose an alternative classification that aligns more closely with the specific requirements of bioprinting, suggesting a tentative size-based division of interconnected pores into 'parvo'-(d < 25 µm), 'medio'-(25 < d < 100 µm), and 'magno'-(d > 100 µm) pores, relying on the current understanding of the pore size role in tissue formation. The introduction of field-specific terminology for pore sizes in 3D bioprinting is essential to enhance the clarity and precision of research communication. This represents a step toward a more cohesive and specialized lexicon that aligns with the unique aspects of bioprinting and tissue engineering.

Polydopamine Blending Increases Human Cell Proliferation in Gelatin-Xanthan Gum 3D-Printed Hydrogel

BACKGROUND

Gelatin-xanthan gum (Gel-Xnt) hydrogel has been previously modified to improve its printability; now, to increase its ability for use as cell-laden 3D scaffolds (bioink), polydopamine (PDA), a biocompatible, antibacterial, adhesive, and antioxidant mussel-inspired biopolymer, has been added (1-3% v/v) to hydrogel.

METHODS

Control (CT) and PDA-blended hydrogels were used to print 1 cm2 grids. The hydrogels' printability, moisture, swelling, hydrolysis, and porosity were tested after glutaraldehyde (GTA) crosslinking, while biocompatibility was tested using primary human-derived skin fibroblasts and spontaneously immortalized human keratinocytes (HaCaT). Keratinocyte or fibroblast suspension (100 µL, 2.5 × 105 cells) was combined with an uncrosslinked CT and PDA blended hydrogel to fabricate cylinders (0.5 cm high, 1 cm wide). These cylinders were then cross-linked and incubated for 1, 3, 7, 14, and 21 days. The presence of cells within various hydrogels was assessed using optical microscopy.

RESULTS AND DISCUSSION

PDA blending did not modify the hydrogel printability or physiochemical characteristics, suggesting that PDA did not interfere with GTA crosslinking. On the other hand, PDA presence strongly accelerated and increased both fibroblast and keratinocyte growth inside. This effect seemed to be linked to the adhesive abilities of PDA, which improve cell adhesion and, in turn, proliferation.

CONCLUSIONS

The simple PDA blending method described could help in obtaining a new bioink for the development of innovative 3D-printed wound dressings.

Synergies in stem cell research: Integrating technologies, strategies, and bionanomaterial innovations

Since the 1960 s, there has been a substantial amount of research directed towards investigating the biology of several types of stem cells, including embryonic stem cells, brain cells, and mesenchymal stem cells. In contemporary times, a wide array of stem cells has been utilized to treat several disorders, including bone marrow transplantation. In recent years, stem cell treatment has developed as a very promising and advanced field of scientific research. The progress of therapeutic methodologies has resulted in significant amounts of anticipation and expectation. Recently, there has been a notable proliferation of experimental methodologies aimed at isolating and developing stem cells, which have emerged concurrently. Stem cells possess significant vitality and exhibit vigorous proliferation, making them suitable candidates for in vitro modification. This article examines the progress made in stem cell isolation and explores several methodologies employed to promote the differentiation of stem cells. This study also explores the method of isolating bio-nanomaterials and discusses their viewpoint in the context of stem cell research. It also covers the potential for investigating stem cell applications in bioprinting and the usage of bionanomaterial in stem cell-related technologies and research. In conclusion, the review article concludes by highlighting the importance of incorporating state-of-the-art methods and technological breakthroughs into the future of stem cell research. Putting such an emphasis on constant innovation highlights the ever-changing character of science and the never-ending drive toward unlocking the maximum therapeutic potential of stem cells. This review would be a useful resource for researchers, clinicians, and policymakers in the stem cell research area, guiding the next steps in this fast-developing scientific concern.

Biopolymers for Tissue Engineering: Crosslinking, Printing Techniques, and Applications

Currently, tissue engineering has been dedicated to the development of 3D structures through bioprinting techniques that aim to obtain personalized, dynamic, and complex hydrogel 3D structures. Among the different materials used for the fabrication of such structures, proteins and polysaccharides are the main biological compounds (biopolymers) selected for the bioink formulation. These biomaterials obtained from natural sources are commonly compatible with tissues and cells (biocompatibility), friendly with biological digestion processes (biodegradability), and provide specific macromolecular structural and mechanical properties (biomimicry). However, the rheological behaviors of these natural-based bioinks constitute the main challenge of the cell-laden printing process (bioprinting). For this reason, bioprinting usually requires chemical modifications and/or inter-macromolecular crosslinking. In this sense, a comprehensive analysis describing these biopolymers (natural proteins and polysaccharides)-based bioinks, their modifications, and their stimuli-responsive nature is performed. This manuscript is organized into three sections: (1) tissue engineering application, (2) crosslinking, and (3) bioprinting techniques, analyzing the current challenges and strengths of biopolymers in bioprinting. In conclusion, all hydrogels try to resemble extracellular matrix properties for bioprinted structures while maintaining good printability and stability during the printing process.

Hydrogel Bioinks of Alginate and Curcumin-Loaded Cellulose Ester-Based Particles for the Biofabrication of Drug-Releasing Living Tissue Analogs

3D bioprinting is a versatile technique that allows the fabrication of living tissue analogs through the layer-by-layer deposition of cell-laden biomaterials, viz. bioinks. In this work, composite alginate hydrogel-based bioinks reinforced with curcumin-loaded particles of cellulose esters (CEpCUR) and laden with human keratinocytes (HaCaT) are developed. The addition of the CEpCUR particles, with sizes of 740 ± 147 nm, improves the rheological properties of the inks, increasing their shear stress and viscosity, while preserving the recovery rate and the mechanical and viscoelastic properties of the resulting fully cross-linked hydrogels. Moreover, the presence of these particles reduces the degradation rate of the hydrogels from 26.3 ± 0.8% (ALG) to 18.7 ± 1.3% (ALG:CEpCUR_10%) after 3 days in the culture medium. The 3D structures printed with the ALG:CEpCUR inks reveal increased printing definition and the ability to release curcumin (with nearly 70% of cumulative release after 24 h in PBS). After being laden with HaCaT cells (1.2 × 106 cells mL-1), the ALG:CEpCUR bioinks can be successfully 3D bioprinted, and the obtained living constructs show good dimensional stability and high cell viabilities at 7 days post-bioprinting (nearly 90%), confirming their great potential for application in fields like wound healing.

3D double-reinforced graphene oxide - nanocellulose biomaterial inks for tissue engineered constructs

The advent of improved fabrication technologies, particularly 3D printing, has enabled the engineering of bone tissue for patient-specific healing and the fabrication of in vitro tissue models for ex vivo testing. However, inks made from natural polymers often fall short in terms of mechanical strength, stability, and the induction of osteogenesis. Our research focused on developing novel printable formulations using a gelatin/pectin polymeric matrix that integrate synergistic reinforcement components i.e. graphene oxide (GO) and oxidized nanocellulose fibers (CNF). Using 3D printing technology and the aforementioned biomaterial composite inks, bone-like scaffolds were created. To simulate critical-sized flaws and demonstrate scaffold fidelity, 3D scaffolds were successfully printed using formulations with varied GO concentrations (0.25, 0.5, and 1% wt with respect to polymer content). The addition of GO to hydrogel inks enhanced not only the compressive modulus but also the printability and scaffold fidelity compared to the pure colloid-gelatin/pectin system. Due to its strong potential for 3D bioprinting, the sample containing 0.5% GO is shown to have the greatest perspectives for bone tissue models and tissue engineering applications.

3D Cell Models in Radiobiology: Improving the Predictive Value of In Vitro Research

Cancer is intrinsically complex, comprising both heterogeneous cellular composition and extracellular matrix. In vitro cancer research models have been widely used in the past to model and study cancer. Although two-dimensional (2D) cell culture models have traditionally been used for cancer research, they have many limitations, such as the disturbance of interactions between cellular and extracellular environments and changes in cell morphology, polarity, division mechanism, differentiation and cell motion. Moreover, 2D cell models are usually monotypic. This implies that 2D tumor models are ineffective at accurately recapitulating complex aspects of tumor cell growth, as well as their radiation responses. Over the past decade there has been significant uptake of three-dimensional (3D) in vitro models by cancer researchers, highlighting a complementary model for studies of radiation effects on tumors, especially in conjunction with chemotherapy. The introduction of 3D cell culture approaches aims to model in vivo tissue interactions with radiation by positioning itself halfway between 2D cell and animal models, and thus opening up new possibilities in the study of radiation response mechanisms of healthy and tumor tissues.

The current state of the art in gellan-based printing inks in tissue engineering

With the advancement of enhanced fabrication technologies, specifically 3D printing, it is now possible to build artificial tissue for personalized healing. However, inks developed from polymers often fail to meet expectations in terms of mechanical strength, scaffold integrity, and the stimulation of tissue formation. Developing new printable formulations as well as adapting existing printing methods is an essential aspect of contemporary biofabrication research. In order to push the boundaries of the printability window, various strategies have been developed employing gellan gum. This has resulted in major breakthroughs in the development of 3D hydrogels scaffolds that exhibit significant resemblance to genuine tissues and enables the fabrication of more complex systems. In light of the many uses of gellan gum, the purpose of this paper is to provide a synopsis of the printable ink designs drawing attention to the various compositions and fabrication approaches that may be used for tuning the properties of 3D printed hydrogels for tissue engineering applications. The purpose of this article is to outline the development of gellan-based 3D printing inks and to encourage research by highlighting the possible applications of gellan gum.

Global hotspots and emerging trends in 3D bioprinting research

Three-dimensional (3D) bioprinting is an advanced tissue engineering technique that has received a lot of interest in the past years. We aimed to highlight the characteristics of articles on 3D bioprinting, especially in terms of research hotspots and focus. Publications related to 3D bioprinting from 2007 to 2022 were acquired from the Web of Science Core Collection database. We have used VOSviewer, CiteSpace, and R-bibliometrix to perform various analyses on 3,327 published articles. The number of annual publications is increasing globally, a trend expected to continue. The United States and China were the most productive countries with the closest cooperation and the most research and development investment funds in this field. Harvard Medical School and Tsinghua University are the top-ranked institutions in the United States and China, respectively. Dr. Anthony Atala and Dr. Ali Khademhosseini, the most productive researchers in 3D bioprinting, may provide cooperation opportunities for interested researchers. Tissue Engineering Part A contributed the largest publication number, while Frontiers in Bioengineering and Biotechnology was the most attractive journal with the most potential. As for the keywords in 3D bioprinting, Bio-ink, Hydrogels (especially GelMA and Gelatin), Scaffold (especially decellularized extracellular matrix), extrusion-based bioprinting, tissue engineering, and in vitro models (organoids particularly) are research hotspots analyzed in the current study. Specifically, the research topics "new bio-ink investigation," "modification of extrusion-based bioprinting for cell viability and vascularization," "application of 3D bioprinting in organoids and in vitro model" and "research in personalized and regenerative medicine" were predicted to be hotspots for future research.

Extraction, Modification and Biomedical Application of Agarose Hydrogels: A Review

Numerous compounds present in the ocean are contributing to the development of the biomedical field. Agarose, a polysaccharide derived from marine red algae, plays a vital role in biomedical applications because of its reversible temperature-sensitive gelling behavior, excellent mechanical properties, and high biological activity. Natural agarose hydrogel has a single structural composition that prevents it from adapting to complex biological environments. Therefore, agarose can be developed into different forms through physical, biological, and chemical modifications, enabling it to perform optimally in different environments. Agarose biomaterials are being increasingly used for isolation, purification, drug delivery, and tissue engineering, but most are still far from clinical approval. This review classifies and discusses the preparation, modification, and biomedical applications of agarose, focusing on its applications in isolation and purification, wound dressings, drug delivery, tissue engineering, and 3D printing. In addition, it attempts to address the opportunities and challenges associated with the future development of agarose-based biomaterials in the biomedical field. It should help to rationalize the selection of the most suitable functionalized agarose hydrogels for specific applications in the biomedical industry.

High resolution and fidelity 3D printing of Laponite and alginate ink hydrogels for tunable biomedical applications

The formulation of hydrogels that meet the necessary flow characteristics for their extrusion-based 3D printing while providing good printability, resolution, accuracy and stability, requires long development processes. This work presents the technological development of a hydrogel-based ink of Laponite and alginate and evaluates its printing capacity. As a novelty, this article reports a standardizable protocol to quantitatively define the best printing parameters for the development of novel inks, providing new printability evaluation parameters such as the Printing Accuracy Escalation Index. As a result, this research develops a printable Laponite-Alginate hydrogel that presents printability characteristics. This ink is employed for the reproducible manufacture of 3D printed scaffolds with versatile and complex straight or curved printing patterns for a better adaptation to different final applications. Obtained constructs prove to be stable over time thanks to the optimization of a curing process. In addition, the study of the swelling and degradation behavior of the Laponite and alginate 3D printed scaffolds in different culture media allows the prediction of their behavior in future in vitro or in vivo developments. Finally, this study demonstrates the absence of cytotoxicity of the printed formulations, hence, setting the stage for their use in the field of biomedicine.

Classification, processing, and applications of bioink and 3D bioprinting: A detailed review

With the advancement in 3D bioprinting technology, cell culture methods can design 3D environments which are both, complex and physiologically relevant. The main component in 3D bioprinting, bioink, can be split into various categories depending on the criterion of categorization. Although the choice of bioink and bioprinting process will vary greatly depending on the application, general features such as material properties, biological interaction, gelation, and viscosity are always important to consider. The foundation of 3D bioprinting is the exact layer-by-layer implantation of biological elements, biochemicals, and living cells with the spatial control of the implantation of functional elements onto the biofabricated 3D structure. Three basic strategies underlie the 3D bioprinting process: autonomous self-assembly, micro tissue building blocks, and biomimicry or biomimetics. Tissue engineering can benefit from 3D bioprinting in many ways, but there are still numerous obstacles to overcome before functional tissues can be produced and used in clinical settings. A better comprehension of the physiological characteristics of bioink materials and a higher level of ability to reproduce the intricate biologically mimicked and physiologically relevant 3D structures would be a significant improvement for 3D bioprinting to overcome the limitations.

Research Progress in Enzymatically Cross-Linked Hydrogels as Injectable Systems for Bioprinting and Tissue Engineering

Hydrogels have been developed for different biomedical applications such as in vitro culture platforms, drug delivery, bioprinting and tissue engineering. Enzymatic cross-linking has many advantages for its ability to form gels in situ while being injected into tissue, which facilitates minimally invasive surgery and adaptation to the shape of the defect. It is a highly biocompatible form of cross-linking, which permits the harmless encapsulation of cytokines and cells in contrast to chemically or photochemically induced cross-linking processes. The enzymatic cross-linking of synthetic and biogenic polymers also opens up their application as bioinks for engineering tissue and tumor models. This review first provides a general overview of the different cross-linking mechanisms, followed by a detailed survey of the enzymatic cross-linking mechanism applied to both natural and synthetic hydrogels. A detailed analysis of their specifications for bioprinting and tissue engineering applications is also included.

Dually crosslinked injectable alginate-based graft copolymer thermoresponsive hydrogels as 3D printing bioinks for cell spheroid growth and release

In this work a dual crosslinked network based on sodium alginate graft copolymer, bearing poly(N-isopropylacrylamide-co-N-tert-butylacrylamide) P(NIPAM-co-NtBAM) side chains was developed and examined as a shear thinning soft gelating bioink. The copolymer was found to undergo a two-step gelation mechanism; in the first step a three-dimensional (3D) network is formed through ionic interactions between the negatively ionized carboxylic groups of the alginate backbone and the positive charges of Ca²⁺ divalent cations, according to the "egg-box" mechanism. The second gelation step occurs upon heating which triggers the hydrophobic association of the thermoresponsive P(NIPAM-co-NtBAM) side chains, increasing the network crosslinking density in a highly cooperative manner. Interestingly, the dual crosslinking mechanism resulted in a five-to-eight-fold improvement of the storage modulus implying reinforced hydrophobic crosslinking above the critical thermo-gelation temperature which is further boosted by the ionic crosslinking of the alginate backbone. The proposed bioink could form arbitrary geometries under mild 3D printing conditions. Last, it is demonstrated that the proposed developed bioink can be further utilized as bioprinting ink and showcased its ability to promote human periosteum derived cells (hPDCs) growth in 3D and their capacity to form 3D spheroids. In conclusion, the bioink, owing its ability to reverse thermally the crosslinking of its polymer network, can be further utilized for the facile recovery of the cell spheroids, implying its promising potential use as cell spheroid-forming template bionk for applications in 3D biofabrication.

Nanofibrillated cellulose/gellan gum hydrogel-based bioinks for 3D bioprinting of skin cells

The development of suitable bioinks is an important research topic in the field of three-dimensional (3D) bioprinting. Herein, novel hydrogel-based bioinks composed of nanofibrillated cellulose (NFC) and gellan gum (GG) in different NFC/GG mass proportions (90:10, 80:20, 70:30, and 60:40) were developed and characterized. The increase in the content of GG, as well as its combination with NFC, enhanced their rheological properties, increasing both storage (G') and loss (G") moduli and the G' recovery capacity of the hydrogels (from 70.05 ± 3.06 % (90:10) to 82.63 ± 1.21 % (60:40)), as well as their mechanical properties, increasing the compressive stiffness and stress from 114.02 ± 10.93 Pa (90:10) to 337.16 ± 34.03 Pa (60:40) and from 18.27 ± 1.32 kPa (90:10) to 47.17 ± 3.59 kPa (60:40), respectively. The hydrogels were non-cytotoxic against human keratinocyte cells (HaCaT), with cell viabilities above 70 % for up to 72 h. The hydrogel 60:40 was loaded with HaCaT cells (3 × 10⁶ cells mL^-1) and bioprinted. The cell viability was maintained elevated until day 7 (90 ± 3 %) after bioprinting. These results highlight that the combination of these two biopolymers was a good strategy for the development of novel hydrogel-based bioinks for extrusion 3D bioprinting applications.

Temperature Induced Gelation and Antimicrobial Properties of Pluronic F127 Based Systems

Different formulations containing Pluronic F127 and polysaccharides (chitosan, sodium alginate, gellan gum, and κ-carrageenan) were investigated as potential injectable gels that behave as free-flowing liquid with reduced viscosity at low temperatures and displayed solid-like properties at 37 °C. In addition, ZnO nanoparticles, lysozyme, or curcumin were added for testing the antimicrobial properties of the thermal-sensitive gels. Rheological investigations evidenced small changes in transition temperature and kinetics of gelation at 37 °C in presence of polysaccharides. However, the gel formation is very delayed in the presence of curcumin. The antimicrobial properties of Pluronic F127 gels are very modest even by adding chitosan, lysozyme, or ZnO nanoparticles. A remarkable enhancement of antimicrobial activity was observed in the presence of curcumin. Chitosan addition to Pluronic/curcumin systems improves their viscoelasticity, antimicrobial activity, and stability in time. The balance between viscoelastic and antimicrobial characteristics needs to be considered in the formulation of Pluronic F127 gels suitable for biomedical and pharmaceutical applications.

Myocardial Cell Preservation from Potential Cardiotoxic Drugs: The Role of Nanotechnologies

Cardiotoxic therapies, whether chemotherapeutic or antibiotic, represent a burden for patients who may need to interrupt life-saving treatment because of serious complications. Cardiotoxicity is a broad term, spanning from forms of heart failure induction, particularly left ventricular systolic dysfunction, to induction of arrhythmias. Nanotechnologies emerged decades ago. They offer the possibility to modify the profiles of potentially toxic drugs and to abolish off-target side effects thanks to more favorable pharmacokinetics and dynamics. This relatively modern science encompasses nanocarriers (e.g., liposomes, niosomes, and dendrimers) and other delivery systems applicable to real-life clinical settings. We here review selected applications of nanotechnology to the fields of pharmacology and cardio-oncology. Heart tissue-sparing co-administration of nanocarriers bound to chemotherapeutics (such as anthracyclines and platinum agents) are discussed based on recent studies. Nanotechnology applications supporting the administration of potentially cardiotoxic oncological target therapies, antibiotics (especially macrolides and fluoroquinolones), or neuroactive agents are also summarized. The future of nanotechnologies includes studies to improve therapeutic safety and to encompass a broader range of pharmacological agents. The field merits investments and research, as testified by its exponential growth.

Cellulose and protein nanofibrils: Singular biobased nanostructures for the design of sustainable advanced materials

Polysaccharides and proteins are extensively used for the design of advanced sustainable materials. Owing to the high aspect ratio and specific surface area, ease of modification, high mechanical strength and thermal stability, renewability, and biodegradability, biopolymeric nanofibrils are gaining growing popularity amongst the catalog of nanostructures exploited in a panoply of fields. These include the nanocomposites, paper and packaging, environmental remediation, electronics, energy, and biomedical applications. In this review, recent trends on the use of cellulose and protein nanofibrils as versatile substrates for the design of high-performance nanomaterials are assessed. A concise description of the preparation methodologies and characteristics of cellulosic nanofibrils, namely nanofibrillated cellulose (NFC), bacterial nanocellulose (BNC), and protein nanofibrils is presented. Furthermore, the use of these nanofibrils in the production of sustainable materials, such as membranes, films, and patches, amongst others, as well as their major domains of application, are briefly described, with focus on the works carried out at the BioPol4Fun Research Group (Innovation in BioPolymer based Functional Materials and Bioactive Compounds) from the Portuguese associate laboratory CICECO-Aveiro Institute of Materials (University of Aveiro). The potential for partnership between both types of nanofibrils in advanced material development is also reviewed. Finally, the critical challenges and opportunities for these biobased nanostructures for the development of functional materials are addressed.

Methods for Biomaterials Printing: A Short Review and Perspective

Printing technologies have opened larger windows of innovation and creativity to biomaterials engineers by providing them with the ability to fabricate complex shapes in a reasonable time, cost, and weight. However, there has always been a trouble to function adjusting in printing technologies in view of the multiplicity of materials and apparatus parameters. 3D printing, also known as additive manufacturing, revolutionized biomaterials engineering by the realization of a digital subject into a printed object (implants, scaffolds, or diagnostics and drug delivery devices/systems).Inspired by the lessons learned from 3D printing, the concept of 4D printing (better called shape-morphing fabrication) was conceptualized and put into practice to reply on the need for responsiveness of printed platforms to an environmental stimulus (light, pH, temperature, voltage, humidity, etc.) in a programmable manner. Later, the next milestone in printing technology was reached by 5D printing, by which objects could be printed from five axes compared to one-point upward printing by 3D printers. 5D printers use ≈20-30% fewer materials comparatively, enabling the printing of curved surfaces. Nevertheless, all bioprinters need a bio-ink with qualifies characteristics for biomedical applications. Thus, we discussed briefly the cell viability, scaffold biomimicry, scaffold biodegradation and affordability.

Advances in 3D Gel Printing for Enzyme Immobilization

Incorporating enzymes with three-dimensional (3D) printing is an exciting new field of convergence research that holds infinite potential for creating highly customizable components with diverse and efficient biocatalytic properties. Enzymes, nature's nanoscale protein-based catalysts, perform crucial functions in biological systems and play increasingly important roles in modern chemical processing methods, cascade reactions, and sensor technologies. Immobilizing enzymes on solid carriers facilitates their recovery and reuse, improves stability and longevity, broadens applicability, and reduces overall processing and chemical conversion costs. Three-dimensional printing offers extraordinary flexibility for creating high-resolution complex structures that enable completely new reactor designs with versatile sub-micron functional features in macroscale objects. Immobilizing enzymes on or in 3D printed structures makes it possible to precisely control their spatial location for the optimal catalytic reaction. Combining the rapid advances in these two technologies is leading to completely new levels of control and precision in fabricating immobilized enzyme catalysts. The goal of this review is to promote further research by providing a critical discussion of 3D printed enzyme immobilization methods encompassing both post-printing immobilization and immobilization by physical entrapment during 3D printing. Especially, 3D printed gel matrix techniques offer mild single-step entrapment mechanisms that produce ideal environments for enzymes with high retention of catalytic function and unparalleled fabrication control. Examples from the literature, comparisons of the benefits and challenges of different combinations of the two technologies, novel approaches employed to enhance printed hydrogel physical properties, and an outlook on future directions are included to provide inspiration and insights for pursuing work in this promising field.

Alginate-Lysozyme Nanofibers Hydrogels with Improved Rheological Behavior, Printability and Biological Properties for 3D Bioprinting Applications

In this study, alginate nanocomposite hydrogel bioinks reinforced with lysozyme nanofibers (LNFs) were developed. Alginate-LNF (A-LNF) suspensions with different LNF contents (1, 5 and 10 wt.%) were prepared and pre-crosslinked with 0.5% (w/v) CaCl₂ to formulate A-LNF inks. These inks exhibit proper shear-thinning behavior and good recovery properties (~90%), with the pre-crosslinking step playing a crucial role. A-LNF fully crosslinked hydrogels (with 2% (w/v) CaCl₂) that mimic 3D printing scaffolds were prepared, and it was observed that the addition of LNFs improved several properties of the hydrogels, such as the morphology, swelling and degradation profiles, and mechanical properties. All formulations are also noncytotoxic towards HaCaT cells. The printing parameters and 3D scaffold model were then optimized, with A-LNF inks showing improved printability. Selected A-LNF inks (A-LNF0 and A-LNF5) were loaded with HaCaT cells (cell density 2 × 10⁶ cells mL⁻¹), and the cell viability within the bioprinted scaffolds was evaluated for 1, 3 and 7 days, with scaffolds printed with the A-LNF5 bioink showing the highest values for 7 days (87.99 ± 1.28%). Hence, A-LNF bioinks exhibited improved rheological performance, printability and biological properties representing a good strategy to overcome the main limitations of alginate-based bioinks.